Add test_installation.sh script (#903)
Add test_installation.sh script (#903)

* Add test_installation.sh script

This script allows to determine if the buster-install-default.sh
installation script works as expected. It does not check *everything*,
but most of the important parts.

* Fix spotify tests, shellcheck errors, result
MiczFlor/RPi-Jukebox-RFID,MiczFlor/RPi-Jukebox-RFID,MiczFlor/RPi-Jukebox-RFID,MiczFlor/RPi-Jukebox-RFID,MiczFlor/RPi-Jukebox-RFID